Searching for a manhwa

I'm searching for a manhwa I read some time ago. It was either a yaoi or a shounen ai. It was some kind of fantasy or supernatural story. The Mc was a man with a superpower but was hiding a part of it and pretended do be an E class or any other weak class even though he clearly was powerful. He encountered Ml who was one of the most powerful during one of the mission they do to train them and all this facility was underground and they couldn't get out of it. I'm sorry if it sounds a bit unnatural but I'm not a native English, I'm sorry for any mistake I made and if anybody is willing to help me, thanks in advance (⌒▽⌒)